Engine systems may include cylinders that exhaust gas to an exhaust pipe and donor cylinders that exhaust gas that is routed to an inlet manifold in what is referred to as Exhaust Gas Recirculation (EGR). One benefit of utilizing donor cylinders is backpressure created from routing EGR gasses to the inlet manifold may be limited to only the donor cylinders, while the remaining cylinders can operate at more efficient exhaust pressure levels. The donor manifold delivers a large pulse of exhaust gas to the inlet manifold one, two, or three times per engine cycle, depending on the number of cylinders attached to a donor cylinder manifold. These exhaust gas pulses may cause variation in an inlet gas stream entering the inlet manifold. Such variation may cause different cylinders to induct different percentages of exhaust gas that may result in air-fuel ratio and combustion inconsistencies leading to higher than optimum fuel consumption and emissions production.
In one approach, recirculated exhaust gas may be mixed with inlet air in a surge tank. The surge tank may be positioned upstream from an inlet manifold. The surge tank may enable exhaust gas to mix with inlet air more uniformly before entering the inlet manifold. Typically, exhaust gas recirculated from a donor cylinder requires a surge tank approximately ten times the cylinder displacement or volume of the donor cylinders in order to achieve uniform mixing of exhaust gas and inlet air.